1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of manufacturing a photo diode.
2. Description of the Related Art
A photo diode based on the theorem of a P-N junction can convert light into an electrical signal. Before light energy in the form of photons strikes the photo diode, there is a depletion layer in the P-N junction and the depletion layer works as an electric field of the capacitor. The electrons in N region do not diffuse to the P region and the holes in the P region do not diffuse to the N region. When enough light strikes the photo diode, the light creates a number of electron-hole pairs. The electrons and the holes diffuse to the P-N junction. As the electrons and the holes reach the P-N junction, the electrons flow to the N region and the holes flow to the P region as a result of the effect of the inner electric field. Thus a current is induced between the P-N junction electrodes. Ideally, a photo diode in the dark is open-circuit. In other words there is no current induced by light energy while the photo diode is in the dark.
Photo diodes are utilized to produce imaging sensors which include charge-coupled device cameras (CCD cameras), PC digital cameras etc. Conventionally, the photo diode usually suffers from plasma damage. Plasma damage is caused by later process steps that include forming an inter-layer dielectric, opening a contact hole, forming a conductive layer, etc. Due to plasma damage, the dark current is uneven, the pixels of the imaging sensors leak irregularly and spots of light occur in the display image.
FIGS. 1A through 1D are schematic, cross-sectional views of a portion of a semiconductor device showing a conventional photo diode.
First, as shown in FIG. 1A, a substrate 100 having a first conductive type is provided. A patterned mask layer 102 is formed on the substrate 100. Thereafter, a LOCOS step is performed to form a field oxide 104 utilized as an isolation region on the substrate 100 exposed by the mask 102.
Referring to FIG. 1B, the mask layer 102 is stripped to expose the surface of the substrate 100 and the isolation region 104. Thereafter, an ion implantation step and an annealing step are utilized to form a doped region 110 having a second conductive type in the active area of the substrate 100 exposed by the isolation region 104.
Next, as shown in FIG. 1C, an inter-layer dielectric layer 112 having a contact hole 116 is formed on the substrate 100 and the isolation region 104, and the contact hole 116 exposes a portion of the active area of the substrate 100. Thereafter, a conductive layer 114 is formed over the substrate 100 and fills the contact hole 116 to form a contact plug 114.
Next, as shown in FIG. 1D, the conductive layer 114 is patterned to form a conductive layer 114a.
Conventionally, plasma damage is caused in the processes of forming the inter-layer dielectric layer, opening the contact hole, forming the conductive layer, etc. Furthermore, the plasma damage leads to uneven dark current, irregular pixel leakage of the imaging sensor, and the spots of light which occur on the display image.
In light of the foregoing, there is a need to provide an improved structure of a photo diode and a method of manufacturing an improved photo diode.